Geissler Tubes

—Tubes of thin gla blown into a great variety of shapes, generally consisting of two bulbs joined by a slender spiral or twisted tube. They are provided with platinum electrodes which are fused into the gla after a partial vacuum has been formed by an air pump, so that by the pa age of an electric discharge through them | under different conditions a great variety of luminous phenomena may be observed. The color of the light depends upon the kind of gla and upon the gas enclosed. Gei ler tubes are sometimes made in beautiful designs. The incandescent lamp is the most common form of the Gei ler tube.